At the present time, the technique of rolling is used to produce products in the form of a continuous strip, especially metal sheets.
To ensure accurate adjustment of the profile of a sheet during rolling, it is possible to act on the camber or convexity of the rolls of the roll stand, particularly the back-up rolls which usually surround the two working rolls of smaller diameter. Many devices have been proposed for this purpose but, to ensure accurate adjustment of the profile of the back-up rolls and of the pressure exerted along the contact generatrix, it was thought useful to provide so-called rolls with a deformable wall, which comprise a fixed central shaft in the form of an elongate beam, onto which is slipped a tubular casing mounted on the shaft so as to be rotatable about its axis by means of bearings located at its ends. Between the inner face of the casing and a bearing face provided on the shaft, there are a plurality of retaining blocks which are aligned in series along the shaft and of which the radial position and the pressure exerted on the inner face of the casing can be adjusted by acting on jacks interposed between each block and the fixed shaft.
In general, each block comprises, for this purpose, a rod which forms a piston and which is mounted slidably in a bore of the shaft forming the body of the jack, the rod being equipped, on the same side as the casing, with a cylindrical bearing face of a radius substantially equal to that of the casing.
Because the fixed block bears on the rotating casing, an oil film has to be placed between the bearing faces of the block and of the casing, and usually the block is provided, on its bearing face, with a recess which forms a pocket and which is supplied with oil under pressure and therefore functions as a result of a hydrostatic effect.
The bearing face of the jack usually covers only a limited part of the casing. However, there has already been a proposal to provide blocks covering a relatively large angular sector of the casing, which can extend virtually up to 180.degree., as indicated, for example, in US-A-No. 3,131,625. If the intention is to arrange a fairly large number of blocks along the contact generatrix, these have a relatively small width which is therefore substantially less than the length of the contact arc, the block thus having a rectangular cross-section. As a result, the block can pivot slightly relative to the bearing point of the thrust jack, and moreover, in U.S. Pat. No. 3,131,625, this bearing point is in the form of a swivel-joint.
However, this pivoting of the block to pivot relative to the jack can have disadvantages, since the block risks becoming askew relative to the casing.
There has also been a proposal, for example in German Offenlegungsschrift No. 2,759,035, to provide blocks covering a relatively long length of the casing, this length being substantially greater than the width of the block.
It can be seen that, in various cases, the retaining blocks can have a rectangular cross-section. If a single jack is used, as in US-A-No. 3,131,625, the width of the working cross-section of the latter cannot exceed the width of the block, and this working cross-section is therefore substantially less than the bearing cross-section of the block on the casing. If the block is to generate a considerable thrust force on the casing, this force being distributed over the rectangular bearing cross-section, the jack must be fed at very high pressure.
To date, such rolls with deformable casings have been used mainly for rolling thin products, such as paper or light metals, and the bearing pressures have not been very high. However, it is now intended to use rolls with deformable casings for rolling sheets, and in this case the bearing pressures on the casing may be much higher. It is therefore expedient to increase the bearing cross-section of the block, making it cover a large annular sector, and at the same time to increase the number of blocks in order to ensure more accurate adjustment. Because of this, each block has a very narrow rectangular cross-section, and, if a single jack is used, it has to be fed at very high pressure, this obviously making the construction of the hydraulic circuits more complicated and more expensive.
It is also possible to associate with each block a larger number of thrust jacks which are distributed over the length of the block and which are fed simultaneously. Such an embodiment was provided, for example, in German Offenlegungsschrift No. 2,759,035, already mentioned, or in GB-No. 2,060,822. This arrangement has the disadvantage of increasing the number of jacks, with their hydraulic circuits, and above all of considerably increasing the length of the seals and consequently the risk of leakage.